During the past few years, the need for accurate and stable standards for determining toxic organics during hazardous waste trial burn tests, compliance source testing, and ambient measurements has become increasingly evident. The scientific and regulatory problems associated with toxic organic pollution cannot be resolved satisfactorily without adequately characterized standards. The USEPA's Atmospheric Research and Exposure Assessment Laboratory has initiated a program to develop stable, accurate organic standards for use in calibration and performance audits. Gaseous organic compounds at parts-per-million (5 to 700 ppm) and parts-per-billion (1 to 10,000 ppb) levels in compressed gas cylinders have been developed. The main objectives of the program are: (1) to provide accurate gas mixtures to assess the relative accuracy of measurement systems during hazardous waste trial burn tests, source compliance testing, and ambient air measurements; (2) to verify the manufacturer's certified analysis of the gas mixtures; and (3) to determine the stability of the organic in compressed gas cylinders. The paper discussed the logic used in selecting organic compounds to develop the cylinder gas approach, summarizes the standards that are currently available plus standards planned for future study, and describes the procedures used to determine the stability of the gaseous compounds in the compressed gas cylinders. The long-term stability data, including the determination of total measurement uncertainty, are also summarized.